One type of earth boring bit has a bit body with three rotatable cones. Each cone has cutting implements for disintegrating earth formations. The cones are mounted on bearing pins that depend from the bit body. A lubricant cavity within the bit body supplies lubricant to the bearing spaces between the cones and bearing pins. A seal or seal assembly is located at the mouth of the cone to prevent loss of the lubricant.
One type of seal is an elastomeric annular member having an inner diameter and an outer diameter. The cross-sectional configuration is rounded, such as circular or elliptical. One of the diameter portions forms a dynamic seal. The dynamic seal portion is in sliding engagement and normally the other side of diameter portion forms a static seal. Sometimes both diameter portions encounter dynamic sealing engagement. The sliding engagement generates heat due to friction, thus causing wear over time.
Some drill bit seals are formed of a single homogeneous elastomeric material. The properties of the elastomeric material are uniform throughout, including at both the inner and outer diameter and interior portions. Another type of drill bit seal is formed of two or more different types of elastomer that are co-cured and bonded together. One type has a greater hardness than the other type for serving as the dynamic seal portion. The softer portion is tailored to provide the desired amount of force due to the squeeze on the seal when installed. The patented prior art also discloses earth boring bit seals with surfaces having different compositions than the interior portion. It has also been proposed to plasma treat the surface of the seal with an inert gas containing a reactive gas species such as chlorine or fluorine. This treatment provides a chlorinated or fluorinated molecules at the surface. Various other techniques to change the surface of an earth boring bit seal are disclosed in the patented art.